1. Field of the Invention
This invention relates generally to the forming of metal structures and relates specifically to the forming of metal structures from the controlled application of layers of molten metal
2. Description of the Prior Art
Metal structures formed by a typical forging process have very high strength. The strength is mainly due to the large numbers of dislocations caused by plastic deformation within the structure during the forging. Forging is normally done by placing metal ingots in hardened dies and using large presses or hammers to apply force to the dies. The dies are usually very expensive and require significant fabrication time. Forged components are used in critical locations, such as aircraft bulkheads, engine crankshafts, or other similar high-load applications.
Due to its low weight and high strength, titanium is used in many aircraft applications. However, the lead time required to obtain titanium ingots may be a year or more. In addition, the forging and machining time may also be a year more, presenting problems when a part is needed quickly for testing or fitting.
In many modern industries, rapid-prototyping is used to create components from materials other than those that will be used to form the final product, for example, a gear formed from plastic rather than from metal. The advantage to rapid prototyping is that a dimensionally-accurate part can be created quickly and inexpensively produced to check for fit within an assembly or other characteristics of the part. Typical rapid-prototype fabrication devices use lasers and computerized solid models to create parts by forming a stack of layers of a material, the layers building upon one another to form the finished part.
Two examples of materials used are photo-reactive liquid polymers and powdered metal. The polymers harden when the laser is directed onto the surface of the liquid. This creates a layer that is a three-dimensional layer of minimal height created from the two-dimensional coordinates provided from the corresponding slice of the solid model. The hardened layer is then lowered below the surface to allow liquid to flow over the hardened areas, and the laser is directed over the surface again to form the next layer, repeating until the last, uppermost layer is formed. A similar process is used with powdered metal, the laser sintering the metal into a solid in layers and building a part by stacking one layer upon the previous layer.
While the rapid prototype process provides dimensionally accurate parts, the parts normally cannot be used as final components, since they lack the desired strength. Thus, there is a need for a method and apparatus for rapidly forming high-strength parts that may be used for testing and fitting or as final components.
A method and apparatus are provided for rapid production of high-strength metal structures. A computerized model of the structure is created, then the model is sliced into horizontal layers. A computer-controlled gantry controls the location of a roller in at least three axes (x, y, and z), the roller depending from the gantry. An electron or laser beam melts the end of a metal wire, forming a puddle of molten metal near the roller. Coordinates defining each layer of the model of the component are sent to the gantry, which moves the roller over the puddle to create a uniform-thickness layer, the wire feeding additional metal to be melted by the beam as the gantry moves. The puddle is narrow, typically requiring multiple narrow strips to be laid adjacent each other to form a complete layer. When a layer is completed, additional layers are formed on the first layer, and this process repeats until the structure is completed.